A way to show others that you are a scared little kid who won't say things to other peoples faces, but will write it in a box on myspace, and not put your identity, because you are scared of getting your ass kicked or rejected.

Lilly: "Oh Ann did you hear what they put in my truthbox?"
Ann: "Yes Lilly, if i would know who they were I'd totally go out with them!"
Mark: "Umm that was me, who put that in your truthbox."
Lilly: *Screams and runs away*